Described below is a device for magnetic bearing of a rotor shaft with respect to a stator having the following features:                a) a first bearing part is connected to the rotor shaft and is surrounded by a second bearing part, which is associated with the stator, with a distance between them,        b) the first bearing part contains rotor disk elements which are aligned at right angles to the axis of the rotor shaft, are arranged one behind the other in the direction of the axis and are each separated, forming an intermediate space,        c) the second bearing part contains stator disk elements, which are aligned at right angles to the rotor shaft axis, are arranged one behind the other in the direction of the rotor axis, are at a distance from one another and each project into one of the intermediate spaces of adjacent rotor disk elements,        d) a magnetic flux directed essentially in the axial direction is formed between the elements.A corresponding bearing device is disclosed, for example, in DE 38 44 563 C2.        
Magnetic bearing devices allow non-contacting and wear-free bearing of moving parts. They require no lubricants and can be designed to have low friction. Known radial and axial magnetic bearing devices use magnetic forces between stationary electromagnets of a stator and ferromagnetic elements which rotate jointly of a rotor body. The magnetic forces are always attractive in the case of this bearing type. In principle, this means that it is impossible to achieve an inherently stable bearing in all three spatial directions. Magnetic bearing devices such as these therefore require active bearing regulation, controlling the currents of electromagnets by position sensors and control loops and counteracting discrepancies of the rotor body from its nominal position. The multichannel regulation to be carried-out requires complex power electronics. Corresponding magnetic bearing devices are used, for example, for turbo molecular pumps, ultra-centrifuges, high-speed spindles for machine tools and X-ray tubes with rotating anodes; they are also known to be used for motors, generators, turbines and compressors.
The basic design of a corresponding bearing device 30 is sketched in FIG. 1. The figure shows two active radial bearings 31 and 32 with excitation magnets 33 and 34 and radial bearing rotor disks 35 and 36 on a rotor shaft 37, an active axial bearing 38 with axial bearing rotor disks 39 and 40 on the rotor shaft 37 and concentric field windings 42i on the rotor disks, as well as five distance sensors 41a to 41e corresponding to the in each case two lateral degrees of freedom per radial bearing and the single degree of freedom of the axial bearing. Furthermore, five associated control loops r1 to r4 and z5 are required. Because the attraction forces increase as the bearing gap becomes smaller in a bearing device such as this, corresponding devices are non-stationary from the start. The position of the rotor shaft 37 must therefore be stabilized by the control loops, comprising distance measurement by the sensors 41a to 41e with a downstream regulator and downstream amplifier, which feeds the excitation magnets 33 and 34. Corresponding bearing devices are accordingly complex. In addition, a mechanical holding bearing must be provided as a precaution against sudden failure of a control loop.
Magnetic bearing devices with permanent magnets and high-Tc superconductor material are also known, for example from DE 44 36 831 C2. Bearing devices such as these are intrinsically stable, that is to say they do not require regulation. However, because of the required cryogenic operating temperature for the superconductor material, in particular of below 80 K, thermal insulation and a refrigerant supply are required by an appropriate cryogenic coolant or by a refrigeration machine.
The related art also includes bearing devices which are intrinsically stable in one direction with a magnetic flux, soft-magnetic parts such as those composed of iron, and with permanent magnets. In corresponding embodiments of bearing devices such as these, such as those disclosed in DE 34 09 047 A1 and the initially cited DE 38 44 563 C2, the permanent magnet rings on a shaft are axially primarily aligned with the poles of an iron yoke, and thus provide radial centering. In this case, the magnetic flux is enhanced by field coils, in which case the axially unstable degree of freedom may be stabilized by an electronic control loop. In this case, a plurality of stationary and rotating ring magnets, which alternate axially one behind the other, are arranged in a row or rows with the same axial magnetization and provide a radial bearing function. In this case as well, the axial degree of freedom must be actively stabilized.
All the bearing devices mentioned above and having permanent-magnet parts have relatively low supporting force and inadequate bearing stiffness, however.